Typically, at each floor of a building there is provided an "up" call button and a "down" call button that a putative passenger can press to request an elevator car. (At the uppermost floor there would only be a "down" button, and at the bottommost floor, or lobby, there would only be an "up" button.) Various schemes have been implemented for assigning particular cars to particular calls, the object being minimizing the overall elevator system response time to all of the car calls. For instance, if there are down car calls entered at the 9th, 10th, 11th, 21st, 22nd, and 23rd floors, one elevator car may be assigned to the 9th, 10th, and 11th floor down car calls while another elevator car is assigned to the 21st, 22nd, and 23rd floor down car calls.
Upon entering a car, the passenger registers a destination call on the car operating panel within the car. This introduces a degree of uncertainty into the system in that the elevator cars could have been more appropriately assigned to the car calls had the passenger's destination (rather than only his desired direction of travel) been known in advance. This degree of uncertainty is manifested in less than optimum overall system response time.
Therefore it has been known, but not widely employed, to provide a "touch pad" at each floor of a building whereby a passenger can enter his ultimate destination prior to the elevator arriving to service his call, rather than only being able to enter a call indicative of his desired direction of travel. Such a system is disclosed in Australian Patent No. 255,218, issued to Leo Port in 1961. A reason for the limited acceptance of a so-called "Port" system, and its derivatives, is that such a system requires touch pads and their associated wiring at each floor, which adds substantial cost to the system hardware and installation.